Various types of bipolar electrolyzers for electrolyzing an alkaline metal chloride aqueous solution such as a salt solution through an ion exchange membrane method have been proposed, for example, in Japanese Patent Disclosure Nos. 51-43377, 58-71382, 62-96688, 5-9770, 9-95792, 10-158875 and 2000-26987.
FIG. 25 is a cross sectional view showing a typical example of an electrolyzer unit which has been used in conventional bipolar electrolyzers.
The conventional electrolyzer unit 100 has an anode chamber 104 constructed of an anode pan 101, anode ribs 102 arranged on a surface of the anode pan 101 and an anode 103 connected to end faces of the anode ribs 102. The anode pan 101, the anode ribs 102 and the anode 103 are made of titanium that has an excellent corrosion resistance.
Also provided is a cathode chamber 108 constructed of a cathode pan 105, cathode ribs 106 arranged on a surface of the cathode pan 105 and a cathode 107 connected to end faces of the cathode ribs 106. The cathode pan 105, the cathode ribs 106 and the cathode 107 are formed of a material with an excellent alkali resistance, such as nickel, stainless steel, iron and iron-nickel alloy (hereinafter referred to as nickel or the like).
Between a back surface of the cathode pan 105 and a back surface of the anode pan 101 are arranged clad plates 111, which are formed by explosion-bonding together a titanium layer 109 and a nickel (or iron) layer 110, with the titanium layer 109 welded to the anode pan 101 and with the nickel layer 110 welded to the cathode pan 105.
These clad plates 111 are interposed between titanium and nickel as it is difficult to weld them directly.
At the top of the anode pan 101 is arranged a partition member 112 of titanium, L-shaped in cross section, which forms an anode-side gas-liquid separation chamber 113. The partition member 112 has an opening 114 in a horizontal surface thereof to ensure flows of liquid and gas into and from the anode chamber 104.
Also at the top of the cathode pan 105 is arranged a partition member 115 of nickel or the like, L-shaped in cross section, which forms a cathode-side gas-liquid separation chamber 116. The partition member 115 has an opening 118 in a horizontal surface thereof to ensure flows of liquid and gas into and from the cathode chamber 108.
The anode ribs 102 and the cathode ribs 106 are both formed with through-holes 119, 120 to ensure flows of the liquid and gas in transverse directions.
The anode pan 101 and the cathode pan 105 have at their periphery flange portions 121, 122 that are bent like a hook. In spaces between the anode-side flange portions 121 and the cathode-side flange portions 122 are installed reinforcing frame members 123 of stainless steel or the like. Front ends of the flange portions 121, 122 engage grooves in the frame members 123.
While FIG. 25 shows only two frame members 123, 123 at the top and bottom, two more frame members are actually provided on the left and right sides of the electrolyzer unit 100.
Among these frame members 123, the one installed at the bottom has a through-hole communicating with the cathode chamber 108, in which hole is installed a nozzle 124 for supplying a liquid. Though not shown in the figure, the frame member 123 has another through-hole communicating with the anode chamber 104, in which is installed a nozzle for liquid supply.
A large number of the electrolyzer units 100 of the above construction are arranged side-by-side in a horizontal direction so that the cathode 107 of one electrolyzer unit and the anode 103 of the adjoining unit oppose each other, as shown in FIG. 26. Between the anode 103 and the cathode 107 are interposed an anode-side seal member 125, a cation exchange membrane 126 and a cathode-side seal member 127. They are pressurized and fixed from the sides by a press machine not shown.
When pure water and refined brine are supplied to the cathode-side nozzle 124 and the anode-side nozzle, respectively, of each electrolyzer unit 100 and a predetermined DC voltage is applied between the anode 103 and the cathode 107, an electrolytic reaction produces chlorine gas and diluted saltwater in the anode chamber 104 and hydrogen gas and a caustic soda aqueous solution in the cathode chamber 108.
Then, the electrolysis products that have reached the gas-liquid separation chambers 113, 116 on the anode and cathode sides are led out through discharge nozzles not shown.
The brine electrolysis process by the ion exchange membrane method has an advantage of having less adverse effects on the environment as compared with the diaphragm method using asbestos and a mercury method.
Referring to FIG. 27 to FIG. 32, the manufacturing process of the conventional electrolyzer unit 100 will be explained.
First, as shown in FIG. 27, a plurality of cathode ribs 106 are arrayed through a jig not shown on a surface 105a of the cathode pan 105 which is formed through bending and welding. A flanged portion 106a of each cathode rib 106 is welded to the surface 105a of the cathode pan 105 by using a DC/AC spot welder.
A lower end portion 106b of each cathode rib 106 is manually TIG-welded to an inner wall surface 105b of the cathode pan 105.
Next as shown in FIG. 28, the cathode pan 105 is turned over, and on its back surface 105c a plurality of clad plates 111 are arrayed at constant intervals and welded to the back surface by the DC/AC spot welder. Then, between the clad plates 111 are arranged reinforcement members 128 made of porous metal which are then TIG-welded to the back surface 105c of the cathode pan.
Then, as shown in FIG. 29, the back surface of the anode pan 101 is placed on the back surface 105c of the cathode pan. As with the cathode pan 105, the anode pan 101 is also formed by bending and welding and has similar vertical and horizontal dimensions to those of the cathode pan.
Next, as shown in FIG. 30, the frame members 123 are successively inserted between the hook-shaped flange portions 121, 122 of the cathode pan 105 and the anode pan 101 along their four sides.
Further, the clad plates 111 are spot-welded to the back surface of the anode pan 101.
Next, as shown in FIG. 31, on a surface 101a of the anode pan 101 a plurality of anode ribs 102 are arrayed through a jig, not shown, and a flanged portion 102a of each anode rib 102 is welded to the anode pan 101 by using the DC/AC spot welder.
TIG-welding is manually effected on the contact between a lower end portion 102b of each anode rib 102 and an inner wall surface 101b of the anode pan 101.
Next, a discharge box 130 is TIG-welded to a notched portion 129 in the flange portion 121 of the anode pan 101. The discharge box 130 is connected with a discharge nozzle 131.
The L-shaped partition member 112 is placed on the anode pan, and a top side 112a, a left side 112b and a right side 112c of the partition member 112 are TIG-welded to the flange portion 121 of the anode pan 101, and a bottom side 112d of the partition member 112 and the surface 101a of the anode pan 101 are TIG-welded to form the anode-side gas-liquid separation chamber 113.
After this, an assembly of the anode pan 101 and the cathode pan 105 is turned over so that the surface 105a of the cathode pan 105 faces up (not shown). As with the anode side, a discharge box 133 and a discharge nozzle 134 are welded to a notched portion 132 of the cathode-side flange portion 122, and the L-shaped partition member 115 is also welded to form the cathode-side gas-liquid separation chamber 116.
Then, as shown in FIG. 32, the cathode-side supply nozzle 124 and the anode-side supply nozzle 135 are mounted in the through-holes of the bottom frame member 123.
Further, the anode 103 (titanium porous plate or meshed material) is placed over the end faces of the anode ribs 102, and they are welded together using a multispot welder.
Moreover, the cathode 107 (nickel porous plate or meshed material) is placed over the end faces of the cathode ribs 106, and they are welded together using the multispot welder. Thus, the electrolyzer unit 100 is completed.
As described above, in the conventional process of manufacturing the electrolyzer unit 100, there are many welding steps. Generally, as the number of welding steps increases, not only do the time and labor increase to that extent but a risk of liquid leakage due to welding failure also becomes high.
Considering the uses of the electrolyzer unit 100, liquid leakage at welding locations are never tolerated. In the conventional manufacturing process, however, since the frame members 123 are inserted at an early stage to combine the anode pan 101 and the cathode pan 105, a problem arises that faulty welding locations cannot be detected effectively.
More specifically, in welded portions between the top side 112a of the anode-side partition member 112 and the flange portion 121 of the anode pan 101 or in welded portions between the top side 115a of the cathode-side partition member 115 and the flange portion 122 of the cathode pan 105, checks from the inside cannot be made at all because the frame members 123 are already inserted between the flange portions 121, 122 at the time of welding although these locations easily develop cracks and holes due to defective welding. The only check that can be made is from the outside. Such is the present situation in welded portions. A similar problem arises with the welding between the lower end portion 102b of each anode rib and the inner wall surface 101b of the anode pan.
Further, in the conventional method of manufacturing the electrolyzer unit 100, because the anode pan 101 and the cathode pan 105 are combined together by inserting the frame members 123 at an early stage and parts such as the discharge boxes 130, 133 and the partition members 112, 115 are assembled into these pans, it is necessary to turn over the assembly of the cathode pan 105 and the anode pan 101 a number of times. This degrades the handling performance. Although the anode pan 101 and the cathode pan 105 are as thin as 1 mm to several mm, the vertical and horizontal dimensions reach 1.2 m×2.4 m or greater and their total weight is significantly large.
The present invention has been accomplished to solve the above problems in the manufacturing process of the conventional electrolyzer unit. An object of the invention is to improve the structure of the electrolyzer unit itself and its manufacturing process to realize the facilitation of detection of defective welding and a reduction in the number of welding locations and to improve the welding method and welding system, thereby enhancing the efficiency of manufacturing the electrolyzer unit.